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Design and performance prediction of hybrid air foil thrust bearings / Donghyun Lee in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 133 N° 4 (Avril 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 4 (Avril 2011) . - 13 p. Titre : Design and performance prediction of hybrid air foil thrust bearings Type de document : texte imprimé Auteurs : Donghyun Lee, Auteur ; Daejong Kim, Auteur Année de publication : 2012 Article en page(s) : 13 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Aerospace  components  Aerospace  engines  Damping  Design  engineering  Elasticity  Finite  difference  methods  Friction  Hydrostatics  Machine  bearings  Orifices  (mechanical)  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air foil bearings (AFBs) have been recognized as the most promising for oil-free turbomachinery. However, the applications of AFBs to the relatively large turbomachinery have many technical challenges due to limited load capacity and wear during start/stops. A hybrid air foil bearing (HAFB), which combines the benefits of AFB and hydrostatic air bearing, was introduced earlier by the authors, and the experimental studies showed much larger load capacity at low speeds and much lesser friction torque during start/stop than hydrodynamic counterpart. The benefit of HAFB was recognized through the experimental studies, and the concept of hybrid operation was further developed to thrust air foil bearings. This paper presents novel design features of the hybrid air foil thrust bearing (HAFTB) with radially arranged bump foils and preformed Rayleigh step contour, and presents simulated static and dynamic characteristics of the HAFTB. A 2D thin plate equation in cylindrical coordinate was solved with the finite difference method for the prediction of the top foil deflection. Parametric studies were performed to evaluate the effect of various design parameters on the static and dynamic performances of HAFTB. At low speeds, a design with orifice located at the center of land region showed the highest load capacity, while a design with orifice located near the leading edge of land region showed the highest load capacity at high speeds. Direct and coupled bearing coefficients were also calculated for various operating conditions. The direct stiffness increases with supply pressure but the direct damping decreases with supply pressure. In addition, typical hardening effect of gas film accompanying increase of stiffness and decrease of damping was predicted in high frequency excitations. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...] [article] Design and performance prediction of hybrid air foil thrust bearings [texte imprimé] / Donghyun Lee, Auteur ; Daejong Kim, Auteur . - 2012 . - 13 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 4 (Avril 2011) . - 13 p. Mots-clés : Aerospace  components  Aerospace  engines  Damping  Design  engineering  Elasticity  Finite  difference  methods  Friction  Hydrostatics  Machine  bearings  Orifices  (mechanical)  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air foil bearings (AFBs) have been recognized as the most promising for oil-free turbomachinery. However, the applications of AFBs to the relatively large turbomachinery have many technical challenges due to limited load capacity and wear during start/stops. A hybrid air foil bearing (HAFB), which combines the benefits of AFB and hydrostatic air bearing, was introduced earlier by the authors, and the experimental studies showed much larger load capacity at low speeds and much lesser friction torque during start/stop than hydrodynamic counterpart. The benefit of HAFB was recognized through the experimental studies, and the concept of hybrid operation was further developed to thrust air foil bearings. This paper presents novel design features of the hybrid air foil thrust bearing (HAFTB) with radially arranged bump foils and preformed Rayleigh step contour, and presents simulated static and dynamic characteristics of the HAFTB. A 2D thin plate equation in cylindrical coordinate was solved with the finite difference method for the prediction of the top foil deflection. Parametric studies were performed to evaluate the effect of various design parameters on the static and dynamic performances of HAFTB. At low speeds, a design with orifice located at the center of land region showed the highest load capacity, while a design with orifice located near the leading edge of land region showed the highest load capacity at high speeds. Direct and coupled bearing coefficients were also calculated for various operating conditions. The direct stiffness increases with supply pressure but the direct damping decreases with supply pressure. In addition, typical hardening effect of gas film accompanying increase of stiffness and decrease of damping was predicted in high frequency excitations. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...]

Design of three-pad hybrid air foil bearing and experimental investigation on static performance at zero running speed / Daejong Kim in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 132 N° 12 (Décembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 12 (Décembre 2010) . - 10 p. Titre : Design of three-pad hybrid air foil bearing and experimental investigation on static performance at zero running speed Type de document : texte imprimé Auteurs : Daejong Kim, Auteur ; Donghyun Lee, Auteur Année de publication : 2011 Article en page(s) : 10 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Aerospace  components  Hydrostatics  Machine  bearings  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air foil bearings (AFBs) have been explored for various micro- to midsized turbomachinery for decades, and many successful applications of the AFBs to small turbomachinery were also reported. As machine size increases, however, one of the critical technical challenges of AFBs is a wear on the top foil and rotor during starts/stops due to relatively heavy rotor weight compared with the size of the bearing. The wear on the foil increases with greater loading during starts/stops as a function of the coating performance. The hybrid air foil bearing (HAFB), which combines hydrodynamic pressure with hydrostatic lift, can help to minimize/eliminate the wear problem during the start/stops. This paper reports design and preliminary test results of hydrodynamically preloaded three-pad HAFB aimed for midsized airborne turbomachinery applications. Designed HAFB was manufactured and comprehensive parametric design simulations were performed using time-domain orbit simulations and frequency-domain linear perturbation analyses to predict performances of manufactured bearing. Static stiffness was measured at zero running speed to investigate the load capacity of hydrostatic operation when rotor is at stationary. The measured static stiffness showed good agreement with predictions. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...] [article] Design of three-pad hybrid air foil bearing and experimental investigation on static performance at zero running speed [texte imprimé] / Daejong Kim, Auteur ; Donghyun Lee, Auteur . - 2011 . - 10 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 12 (Décembre 2010) . - 10 p. Mots-clés : Aerospace  components  Hydrostatics  Machine  bearings  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Air foil bearings (AFBs) have been explored for various micro- to midsized turbomachinery for decades, and many successful applications of the AFBs to small turbomachinery were also reported. As machine size increases, however, one of the critical technical challenges of AFBs is a wear on the top foil and rotor during starts/stops due to relatively heavy rotor weight compared with the size of the bearing. The wear on the foil increases with greater loading during starts/stops as a function of the coating performance. The hybrid air foil bearing (HAFB), which combines hydrodynamic pressure with hydrostatic lift, can help to minimize/eliminate the wear problem during the start/stops. This paper reports design and preliminary test results of hydrodynamically preloaded three-pad HAFB aimed for midsized airborne turbomachinery applications. Designed HAFB was manufactured and comprehensive parametric design simulations were performed using time-domain orbit simulations and frequency-domain linear perturbation analyses to predict performances of manufactured bearing. Static stiffness was measured at zero running speed to investigate the load capacity of hydrostatic operation when rotor is at stationary. The measured static stiffness showed good agreement with predictions. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...]

Thermohydrodynamic analyses of bump air foil bearings with detailed thermal model of foil structures and rotor / Donghyun Lee in Transactions of the ASME . Journal of tribology, Vol. 132 N° 2 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 132 N° 2 (Avril 2010) . - 12 p. Titre : Thermohydrodynamic analyses of bump air foil bearings with detailed thermal model of foil structures and rotor Type de document : texte imprimé Auteurs : Donghyun Lee, Auteur ; Daejong Kim, Auteur Année de publication : 2011 Article en page(s) : 12 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Convection  Foils  Machine  bearings  Rotors  Turbomachinery Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A new thermohydrodynamic analysis model for bump air foil bearings with a detailed thermal model of bump foil structures and rotor is presented. In the developed model, temperatures of lubricating air film, top foil, bump foils, bearing sleeve, and rotor are calculated simultaneously through an iterative process. Reynolds equation and 3D energy equation were applied to the air film, and energy equations were applied to all the other structures around the bearing. Energy and momentum equations were applied to cooling channels to predict spatial temperature distribution along the cooling channels. The thermal growth of the rotor, foil structure, bearing sleeve, and centrifugal growth of the rotor are also considered. For the accuracy of the model, effective heat transfer resistance between the top foil and bearing sleeve was measured for various conditions and implemented into the thermal analysis around the cooling channels. The model was also bench marked with published experimental results for verifications. Using a developed model, parametric studies were performed with different bearing nominal clearances, applied loads, rotating speeds, and cooling conditions through channels. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Thermohydrodynamic analyses of bump air foil bearings with detailed thermal model of foil structures and rotor [texte imprimé] / Donghyun Lee, Auteur ; Daejong Kim, Auteur . - 2011 . - 12 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 132 N° 2 (Avril 2010) . - 12 p. Mots-clés : Convection  Foils  Machine  bearings  Rotors  Turbomachinery Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A new thermohydrodynamic analysis model for bump air foil bearings with a detailed thermal model of bump foil structures and rotor is presented. In the developed model, temperatures of lubricating air film, top foil, bump foils, bearing sleeve, and rotor are calculated simultaneously through an iterative process. Reynolds equation and 3D energy equation were applied to the air film, and energy equations were applied to all the other structures around the bearing. Energy and momentum equations were applied to cooling channels to predict spatial temperature distribution along the cooling channels. The thermal growth of the rotor, foil structure, bearing sleeve, and centrifugal growth of the rotor are also considered. For the accuracy of the model, effective heat transfer resistance between the top foil and bearing sleeve was measured for various conditions and implemented into the thermal analysis around the cooling channels. The model was also bench marked with published experimental results for verifications. Using a developed model, parametric studies were performed with different bearing nominal clearances, applied loads, rotating speeds, and cooling conditions through channels. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]

Transient thermal behavior of preloaded three-pad foil bearings / Donghyun Lee in Transactions of the ASME . Journal of tribology, Vol. 133 N° 2 (Avril 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 133 N° 2 (Avril 2011) . - 11 p. Titre : Transient thermal behavior of preloaded three-pad foil bearings : modeling and experiments Type de document : texte imprimé Auteurs : Donghyun Lee, Auteur ; Daejong Kim, Auteur ; Ramesh P. Sadashiva, Auteur Année de publication : 2012 Article en page(s) : 11 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Convection  Electric  power  generation  Fuel  cells  Machine  bearings  Rotors  Solar  cells  Stability  Turbomachinery Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Oil-free turbomachinery have emerged as one of the core technologies for the future green power generation systems as stand-alone systems or hybridized with high temperature fuel cells or solar systems. Oil-free technology allows compact, clean, and maintenance-free operation, and foil bearings are at the center of the technology. Since their first commercial applications in the air cycle machines and auxiliary power units in 1970s, significant improvement has been made to the computational models for rotordynamic behavior. However, many technical issues still remain unsolved or poorly understood, and one of them is thermal management. This paper presents transient three-dimensional thermohydrodynamic (3D THD) model of radial foil bearings to predict transient thermal behavior of the bearing-rotor system. The transient model involves transient energy equations applied to all the mechanical structures and gas film. The model was verified through extensive experimental measurements of transient thermal behavior of three-pad foil bearing for various cooling air pressures, external loads, and speeds. The predictions showed very good agreements with the experiments, and also the 3D THD model could predict potential thermal instability observed in the experimental measurements. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Transient thermal behavior of preloaded three-pad foil bearings : modeling and experiments [texte imprimé] / Donghyun Lee, Auteur ; Daejong Kim, Auteur ; Ramesh P. Sadashiva, Auteur . - 2012 . - 11 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 133 N° 2 (Avril 2011) . - 11 p. Mots-clés : Convection  Electric  power  generation  Fuel  cells  Machine  bearings  Rotors  Solar  cells  Stability  Turbomachinery Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Oil-free turbomachinery have emerged as one of the core technologies for the future green power generation systems as stand-alone systems or hybridized with high temperature fuel cells or solar systems. Oil-free technology allows compact, clean, and maintenance-free operation, and foil bearings are at the center of the technology. Since their first commercial applications in the air cycle machines and auxiliary power units in 1970s, significant improvement has been made to the computational models for rotordynamic behavior. However, many technical issues still remain unsolved or poorly understood, and one of them is thermal management. This paper presents transient three-dimensional thermohydrodynamic (3D THD) model of radial foil bearings to predict transient thermal behavior of the bearing-rotor system. The transient model involves transient energy equations applied to all the mechanical structures and gas film. The model was verified through extensive experimental measurements of transient thermal behavior of three-pad foil bearing for various cooling air pressures, external loads, and speeds. The predictions showed very good agreements with the experiments, and also the 3D THD model could predict potential thermal instability observed in the experimental measurements. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]